I have installed Armbian 25.02 via an official Armbian image for Armbian 25.02 (Debian 12) Vendor Kernel 6.1.xx, is it possible (and sane) to upgrade to Armbian 25.05 (Debian 12) Vendor Kernel 6.1.xx? If so besides downloading the new image and installing fresh what are one's options?

What is your goal?  25.02 is a stable release.  There is no 25.05 stable release yet (that will happen towards the end of next month).  So what is out there now are daily development rolling builds of 20.05.  So if you want to track development then this would make sense (note the use 0f the word 'daily' there, things can change that often, and these changes aren't well tested yet), but if you want tested stability then you should wait until the next stable release comes out.